In recent years, retail and wholesale merchandisers have directed substantial attention to the nagging and costly problem associated with the theft and/or damage of costly display products on their premises. With the advent of smaller and more portable electronic apparatus, the ease with which pilferers and shoplifters can quickly and easily remove such goods from display cases and display racks has intensified. At the same time, the availability of new products, such as video cassette recorders, small portable radios and televisions, calculators and the like has skyrocketed, resulting in more and more valuable products being taken or tampered with. As locks and other security devices have become more sophisticated, so too have the individuals and methods for circumventing the operation of conventional security devices and, particularly, alarm sensing devices. For example, conventional sensor devices can be circumvented by artful replacement of an exposed or otherwise slidable conducting means utilized in such devices by an alternative conducting means, such as a small electrical conducting plate, resulting in the theft of the "protected" article. Mass merchandisers often end up returning to a display case or rack only to find the otherwise reliable alarm sensor waylaid by a short-circuiting plate, which was effectively shifted into position to replace the closed circuit conductor previously attached (or which may still be attached) to the article stolen just minutes earlier.
One solution to the above-mentioned problems is shown in commonly-assigned U.S. Pat. No. 4,455,464, dated Jun. 19, 1984, which discloses an alarm system having an electrical conductor connected at one end to the alarm sensor. A plurality of sensors are connected in series to the electrical conductor. An electrical conductor connects the last sensor back to the alarm system. The sensors complete an electrical circuit which is monitored. The alarm system continually checks the sensors to determine if they have been removed from the product or tampered with. However, when one of the sensors has been removed or tampered with, it is difficult to determine which sensor. Furthermore, upon connecting each of the sensors to the products and back to the alarm circuit, it is difficult to determine if a sensor has been improperly connected to a product. Thus, when the alarm is enabled, the alarm will sound if the sensors are incorrectly applied.
The present invention provides an alarm system having sensors including an indicating means, for example, a light-emitting diode, which indicates the state of each sensor.